It is known, for example from British patent 2298370 to provide a rapidly changing magnetic field, of the order of 20 kiloteslas per second, in the vicinity of tissue in order to induce electric current in the tissue and thereby stimulate the tissue.
Known magnetic stimulators comprise generally a charging circuit, a capacitor, a discharge control such as a control rectifier, and a coil which is of a size and power rating appropriate for the generation of the very large magnetic fields which magnetic stimulators require. Typically, the coil may be of a size adapted to fit partly over the cranium of a human patient. Others forms of coil are, as exemplified herein, in the shape of a large figure of eight.
In the aforementioned patent and also in U.S. Pat. Nos. 5,718,662 and 5766124 there are described stimulators which are capable of providing a rapid sequence of discharge pulses through the stimulating coil. Such a rapid sequence of pulses is useful in, for example, transcranial magnetic stimulation.
However, owing to the very large energy contained in the pulses, such a stimulation technique is very liable to produce overheating of a stimulating coil. It is known to provide in a stimulating system of this general nature, some means of monitoring the temperature in the vicinity of a stimulating coil and to provide some inhibiting function, such as disabling the stimulating system if a coil should overheat. It is customary to change coils in those circumstances.
The present invention has the general object of avoiding the need to change coils unnecessarily and is based on a coil design which allows cooling by the flow of a coolant gas around substantially all the exposed surfaces of the stimulating coil and preferably also a supply cable to it.
Other features and advantages of the invention will be apparent from the accompanying drawings.